Engine crankcase explosions on ships happens a few times every year and since they regularly lead to the dead of engine personal and to large damages of the engine and the surrounding engine room, many efforts are made to avoid explosion. Crankcase explosions can occur when oil mist is formed inside the engine. Oil mist is highly explosive and can be ignited by a hot spot of the engine. If a component inside the engine runs hot lubricating oil on the component evaporates and condensates into small droplets in colder areas, hereby forming the aforementioned oil mist. The mist can be ignited by the same component creating the mist. When mist explosions happen inside the engine the resultant pressure wave can propagate large amounts of unburned oil outside the engine where it can be ignited by other sources and contribute further to the effects of the preceding explosion.
Oil mist detectors are used in the shipping industry to detect the existence of oil mist. However mist detectors suffer from a large number of false alarms and since the avoidance of further oil mist creation is remedied by reducing the engine load or stopping the engine, a ship will consequently have reduced manoeuvrability, which e.g. during harbour manoeuvring could lead to collisions. A reduction in the number of false alarms is therefore highly requested by the shipping industry. Further more are oil mist detectors relatively expensive.
Besides oil mist generating faults are also faults creating blow-by gas, which increase the pressure in the crankcase, forming part of the engine housing, detectable. Blow-by gases enter the crankcase through clearances around the piston rings.
EP777041 discloses a sensor for detection of blow-by gasses in an engine making it possible to evaluate the performance of an engine. The sensor combines a venturi with a differential pressure sensor. The pressure sensor receives inputs from two positions in the venture and based on the pressure difference is the performance of the engine evaluated.
A different approach for detection of faults generating increased pressure in the engine housing is disclosed in FR2641575. Here is a manometer with a photo detection system is used. One side to the manometer is connected to the engine housing, while the other side is connected to the engine room atmosphere. Between the two tube legs of the manometer is a flow restriction to avoid up and down movement of manometer fluid caused by the rocking of a ship. When then pressure difference reaches a certain limit detected by the photo detection system this is considered to indicated an upcoming engine fault. More or less similar systems are disclosed in NL6600131 and JP4019312. These systems have not gained a wide spread use within the shipping industry. One reason could be that they are prone to false alarms. False alarms will be generated when the pressure in the engine room falls. This will be detected as an increased pressure differential, but will generally not be cause by engine faults. Such pressure drops will happen, when an access entry to the engine room fx. a door, is opened, because the pressure in the engine room is higher than the atmospheric pressure present in the rest of a ship. Higher pressure is present because the turbocharger of the engine takes air from the engine room and to ensure sufficient air in the room air is blow into the room.